A variety of methods for preparing and isolating poly(arylene) ether homopolymers and copolymers are well known in the art. Many are described in U.S. Pat. No. 6,407,200. One established method for making the polymers involves precipitating the polymer after the conclusion of the polymerization reaction from the reaction mixture (which is usually in a solvent such as toluene) with a polymer anti-solvent such as methanol or aqueous methanol or the like with agitation (stirring or shaking or the like) and then filtering the resulting precipitate. Such a procedure is often suitable for efficiently producing high yields of the desired poly(arylene ether) polymer product. However, there are some drawbacks to the process. For example, the poly(arylene ether) powder produced by this method sometimes includes an undesirably high proportion of powder “fines”—solid particles having a particle size less than about 38 micrometers (μm).
Fines can be responsible for a variety of problems during subsequent processing of polymers. As a first matter, their presence may be associated with losses of poly(arylene ether) during filtration and drying stages. Also, fines tend to stick to processing line filters, where they can cause clogging and unacceptable variations in line pressure, excessive pressure drops, resulting in increased processing times. Filter pressure drops may trigger alarms, which shut off the powder transport through a transport line, for example, from a resin silo to a silo in a compounding area.
As a second matter, in general, the presence of high powder fines can make it difficult to efficiently separate the polymer powder from gas in drying transport systems, which results in the accumulation of fines in vent systems, and possible dust emissions into the atmosphere. Removal of the fines from the filters can be a difficult and time-consuming task. Moreover, the presence of fines can create dust explosion hazards if powder handling involves contact with air, thus necessitating the installation of expensive safety equipment.
As a third matter, in addition to transport and flow problems, the presence of fines can be problematic during subsequent compounding operations to make formulated products. For example, although they constitute part of the solid powder composition, fines often do not have the minimum solid mass and density values to ensure proper feed into an extruder.
Several approaches to reducing fine particle content during production of poly(arylene ether)s have been reported. For example, a method for preparing a poly(arylene) ether with reduced powder fine levels is also described in U.S. Pat. No. 7,205,377. The method comprises oxidatively coupling a monohydric phenol in the presence of a solvent and a complex metal catalyst, to produce a poly(arylene ether) resin and then removing a portion of the solvent to produce a concentrated solution having a cloud point Tcloud. The concentrated solution is then combined with an anti-solvent to precipitate the poly(arylene ether) in the form of a precipitation mixture. The concentrated solution usually has a temperature of at least about (Tcloud−10° C.) immediately before it is combined with the anti-solvent. The precipitation mixture has a temperature of at least about (Tcloud−40° C.) after its formation.
U.S. Pat. No. 7,151,158 discloses a method of precipitating poly(arylene ether)s with reduced fine particles. The method comprises combining at a shear rate of 50,000 to 500,000 sec−1 a poly(arylene ether) mixture with a solvent to form a dispersion. The filtered, precipitated precipitating poly(arylene ether)s had a substantially lower content of fines
U.S. Pat. No. 6,787,633 discloses an alternative method for precipitating poly(arylene ether)s with reduced fine particles involving adjustment of a single precipitation parameter after the polymer/solvent mixture is combined with the anti-solvent.
U.S. Pat. No. 6,407,200 describes a method of preparing poly(arylene ether)s, wherein a portion of the reaction solvent is removed after the catalyzed oxidative reduction step. Removal of the solvent portion leaves a concentrated solution of the polymer product. This solution is subsequently combined with an anti-solvent, to precipitate the desired polymer product. If the temperature of the concentrated solution is elevated to specified levels immediately before combination with the anti-solvent, the generation of the undesirable fines may be reduced.
U.S. Pat. No. 6,316,592 discloses a method for separating a polymer resin from a solution slurry which uses a precipitation aid such as a linear or branched polymer which absorbs onto the surface of the polymer resin particulates.
Finally, in U.S. Pat. No. 3,923,738, a method is disclosed for preparing polyphenylene ether resins with narrow particle size distribution, higher bulk density and of substantially lower content of dusty, fine particles by precipitation from an organic aromatic solvent with a non-solvent medium which is capable of forming a two-phase system with the aromatic solvent.
Despite these and other approaches, a need remains for a method to produce poly(arylene ether)s with improved particle size characteristics.